1. Field of the Invention
The present invention relates to a portable semiconductor memory unit and, more particularly, it relates to portable semiconductor memory units such as an IC card (memory card) provided with only a semiconductor memory and an IC card provided with a CPU together with a semiconductor memory.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a conventional portable semiconductor memory unit and a system to use it. An IC card 1, which is a kind of portable semiconductor memory unit, is provided with a semiconductor memory 3 such as a one time programmable read only memory (OTPROM) and an electrically erasable programmable read only memory (E.sup.2 PROM) which require different voltages for reading and writing (and erasing). A terminal equipment 2, which is a part of a on-line system, for example, is equipped with an voltage supply circuit 7 for supplying a voltage to the semiconductor memory 3. The voltage supply circuit 7 provides voltages to an operation voltage receiving terminal (Vcc) and a writing voltage receiving terminal (Vpp) of the semiconductor memory 3 installed on the IC card 1. The terminal equipment 2 reads from and writes to the semiconductor memory 3 through a data bus 5 by providing address signals through an address bus 4 and read/write mode and other control signals through a control bus 6.
When the terminal equipment 2 reads data from the semiconductor memory 3 of the IC card 1, the terminal equipment 2 provides the same voltages, for example 5 V, to the operation voltage receiving terminal Vcc and a writing voltage receiving terminal Vpp of the semiconductor memory 3. Thereafter, the terminal equipment 2 provides a read address by the address bus 4, sets a read mode by the control bus 6 and reads data from the semiconductor memory 3 by the data bus 5.
On the other hand, when the terminal equipment 2 writes to the semiconductor memory 3 of the IC card 1, the terminal equipment 2 provides different voltages, for example 6 V and 12.5 V, to the operation voltage receiving terminal Vcc and the writing voltage receiving terminal Vpp of the semiconductor memory 3, respectively. Thereafter, the terminal equipment 2 provides a write address by the address bus 4, sets a write mode by the control bus 6 and writes data to the semiconductor memory 3 by the data bus 5.
Thus, in order to access to the conventional portable semiconductor memory unit such as an IC card, the terminal equipment 2 has to be provided with a dedicated voltage supply circuit 7 capable of generating different voltages when the portable semiconductor memory unit is installed with the semiconductor memory 3 such as PROM and E.sup.2 PROM which need different voltages in reading and writing.